The present invention relates to an inter-axle differential of a vehicle and an inter-axle differential lock for locking the same.
A multiple-axle-driving vehicle, which is a mechanical type and drives a plurality of axles of front and rear wheels and the like, such as an articulated dump truck is conventionally known, and FIG. 1 is a side view thereof. In FIG. 1, output power of an engine 10 is transmitted dividedly to a front differential 15 and rear differentials 16 and 18 via a torque converter 14 and a transmission 11 by a transfer device 12.
The transfer device 12 is provided with an inter-axle differential 13 being a differential device for distributing the output power of the engine 10 to front wheels 2 and rear wheels 4 at a predetermined ratio. The inter-axle differential 13 gives a rotation difference between the front and rear wheels 2 and 4 according to a traveling distance of tires to absorb the rotation difference between the front wheels 2 and the rear wheels 4 when different loads are on the front wheels 2 and the rear wheels 4, for example, during turning, and has a function of making the vehicle travel smoothly.
However, there exist the following disadvantages in travel of the conventional articulated dump truck.
For example, when the dump truck goes uphill with a load thereon, a rear portion of the vehicle body drops while a front portion is raised. As a result, the load ratio of the front and rear wheels 2 and 4 is shifted toward the rear wheels 4. In this situation, if the road surface is soft, or has uneven spots, the front wheels 2 sometimes skid. However, since the inter-axle differential 13 compulsorily distributes torque to the front and rear wheels 2 an 4 at a specified ratio, the torque of the specified ratio out of the output power of the engine 10 is always transmitted to the front wheel 2 in the state in which the inter-axle differential 13 works. For this reason, when the front wheels 2 skid, rotation of the front wheels 2 under lighter load increases more and more to make the front wheels 2 idle.
Further, due to the inter-axle differential 13, the driving force of the entire vehicle depends on the smaller one of the torque transmitted to the road surface from the front wheels 2 and the torque transmitted to the road surface from the rear wheels 4. For this reason, when the front wheels 2 skid, acceleration of the vehicle decreases, and in some cases, the rear wheels 4 stop while only the front wheels 2 vigorously idle, whereby the vehicle stops. Further, when a squat phenomenon, in which the front wheels 2 are raised due to loss of torque as described above, ceases and subsequently the front wheels 2 land on the ground and recover ground contact pressure, a squat is caused by the driving force once again. As a result of the repetition of grip and skid of the front wheels as described above, the vehicle hardly advances, and pitching occurs sometimes, which makes the traveling difficult.
The disadvantages as described above also arise when the dump truck goes downhill in reverse, for example, with a retarder brake being applied. In this situation, load is shifted toward the rear wheels 4 due to brake torque of the retarder brake, and the front wheels 2 of the vehicle are raised, skid, and idle.
The present invention is made in view of the aforementioned disadvantages, and its object is to provide an inter-axle differential capable of preventing a skid to achieve stable travel even in the situation in which load is unevenly distributed.
In order to attain the above object, a control method of the inter-axle differential of the present invention is a control method of an inter-axle differential for distributing torque to front and rear driving wheels at a predetermined ratio, and includes the step of:
monitoring a skid occurring to the driving wheels, and locking the inter-axle differential when a sign of a skid occurring to the driving wheels appears.
As described above, for example, when the vehicle goes uphill with a load carried thereon and when the vehicle reverses downhill with the brake being applied, very large load is exerted on the rear wheels, and thus the front wheels easily skid. Accordingly, by monitoring a skid occurring to the front wheels and taking countermeasures against the skid, for example, stable travel can be achieved.
If a skid occurs, the inter-axle differential is locked and thereby the front wheels and the rear wheels are directly connected. As a result, the rotational frequencies of the front and rear wheels become a predetermined constant rotational frequency irrespective of load. Consequently, it does not happen that the rotational frequency of the front wheels becomes higher and higher though the front wheels are idling, thus increasing the possibility of the front wheels recovering from the skid. Further, since torque is also transmitted to the rear wheels, the vehicle can continue to travel owing to the gripping force. As described above, a skid can be surely prevented, pitching and stopping of the vehicle body can be prevented, and stable travel can be achieved.
An inter-axle differential apparatus of the present invention is an inter-axle differential apparatus including an inter-axle differential for distributing torque to front and rear driving wheels at a predetermined ratio,
an inter-axle differential lock for locking the inter-axle differential, and
a controller for outputting a differential locking signal to the inter axle-differential lock and locking the inter-axle differential, includes
at least any one of the following rotation detectors: a first rotation detector for detecting rotational frequency of a transmission output shaft; a second rotation detector for detecting rotational frequency of a front output shaft of the inter-axle differential; and a third rotation detector for detecting rotational frequency of a rear output shaft of the inter-axle differential, and
the controller detects a sign of a skid occurring to the driving wheels based on at least any one of the following:
rotational frequency detected by at least any one of the rotation detectors; and a rate of change with time of the detected rotational frequency, and outputs the differential locking signal when finding the sign of a skid.
For example, if a skid occurs to the front wheels with load being shifted to the rear wheels, the front wheels repeatedly rise and land on the ground, thus cyclically increasing and decreasing the rotational frequency of the front wheels. Accordingly, by detecting the rotational frequency of the front output shaft of the inter-axle differential, and the amplitude and cycle of the shaft rotation acceleration being the rate of change with time thereof, a sign of a skid can be accurately detected. Further, since the inter-axle differential functions so as to increase and decrease the rotational frequency of the rear output shaft inversely with an increase and decrease in the rotational frequency of the front output shaft, a sign of a skid can be accurately detected by detecting the shaft rotation acceleration being the rate of change with time thereof.
Furthermore, when a skid occurs and the wheels vigorously idle, the total transmission torque to a road surface decreases. As a result, the engine load is decreased, and especially during full-throttle acceleration, the rotation of the engine abruptly becomes high, thereby increasing the rotational frequency of the transmission output shaft. On the other hand, for example, when the axle of the front wheels which are skidding recovers grip as a result of the wheels landing on the ground, engine load torque increases, thus reducing the engine speed. Accordingly, by detecting the rotational frequency of the transmission output shaft and its shaft rotation acceleration, a sign of a skid can be accurately detected.
As described above, by detecting at least any one of the rotational frequencies, a sigh of a skid can be detected. Consequently, the inter-axle differential is locked based on the above, thereby making it possible to surely prevent a skid and recover the normal operation. Since an ordinary vehicle is always equipped with a rotational frequency detector for detecting the rotational frequency of the transmission output shaft, it is not necessary to provide another detector, and a slip can be detected easily.